摘要：
The transmittance diminishment of solar cells, caused by dust accumulation is higher than 52.54% every year (2006 Energ. Convers. Manage. 473192), which greatly reduces their overall efficiencies of power conversion. Any other strategy for improving the photovoltaic device cannot compensate for this loss caused by the dust. However, this critical issue has not received much attention. In this work, a kind of self-cleaning coating consisting of ZnO nanowire-silicon pyramid hierarchical structures is proposed to overcome the dust accumulation on the photovoltaic device. The principle of designing this self-cleaning is based on the Cassie-Baxter theory. Both the micron size effect for superhydrophobicity and the performance of anti-reflection of light of the substrate should be retained, which are the requirements of application of solar cell. The pyramid-like silicon (named "silicon pyramid", hereafter) is fabricated by simple chemical etching. The effects of isopropanol, KOH, etching time, and etching temperature on the morphology of the silicon pyramid are investigated by using systematic statistical design and analysis method, to obtain the best distribution and size of the silicon pyramid. In the systematic statistical design and analysis method, the pick-the-winner rule is adopted. Eventually, we find that the optimized conditions for etching silicon pyramid (according the requirements of self-clean) are as follows: etching time is 60 min, etching temperature is 95 °C, and mixture is 80 mL DI water, 2.9598 g KOH and 20 mL isopropanol. Moreover, ZnO nanowire-silicon pyramid hierarchical structures for the application of photovoltaic device are successfully hydrothermally grown on the substrate of silicon pyramid for the first time. The obtained self-cleaning coating consists of ZnO nanowire (with a diameter of 136 nm) and silicon pyramid (with a size of 8–11 μm). The surface of this coating possesses superhydrophobic properties, i.e., a water contact angle of 154? and a contact angle hysteresis of less than 10?, after being modified by heptadecafluorodecyltrimethoxysilane. Also, our obtained ZnO nanowire-silicon pyramid hierarchical structures have quite a good performance of anti-reflection, which appear gray in the normal environment. And the mechanism for it is postulated. Importantly, some new phenomena, such as"high temperature"improving the growth of silicon pyramid, are also revealed. Besides, the physical mechanism for"high temperature"improving the growth of silicon pyramid and anisotropic etching of silicon substrate is discussed. It is indicated that the anisotropic behavior is attributed to small difference in energy level (being a function of the crystal orientation) between the back-bond surface states. The method we proposed to achieve self-cleaning coating is versatile, reliable and low-cost, which is also compatible with contemporary micro-and nano-fabrication processes.%光伏器件粉尘堆积伴随的遮光效应极其严重,可导致太阳能电池的光电转换效率降低一半以上,这是任何其他提高光伏器件性能的高新技术所不能弥补的.本文根据Cassie-Baxter理论构建出一种基于光伏器件应用的超疏水自清洁微纳复合结构,即氧化锌纳米线耦合硅金字塔.通过调控硅金字塔的尺寸和均匀性,使其尺寸效应不被遮盖以符合存在微米构型的疏水要求,同时尽量不破坏硅光伏器件绒面的减反性能.本文采用水热法在金字塔表面生长氧化锌纳米线的方案,通过系统的实验设计,首次成功地制备了符合光伏器件应用的接触角高达154?,且接触角滞后小于10?的超疏水自清洁微纳复合结构.此外,我们不仅发现硅金字塔的刻蚀存在"高温促进硅金字塔刻蚀"的温度效应和硅金字塔顶部有"圆润-方正-圆润"的时间效应,还从物理上对高温促进刻蚀、晶体的各向异性刻蚀导致的硅金字塔和我们所制备的氧化锌纳米线耦合硅金字塔复合结构的陷光效应等进行了比较充分的分析.
